Apparatus for measuring the thickness of a coating applied to a moving strip



May 21, 1957 w, s 2,793,345

APPARATUS FOR MEASURING THE THICKNESS OF A COATING APPLIED TO A MOVINGSTRIP Filed 001 29, 1955 UNCOATED-STR/P COATED-STRIP MEASURING GAGEMEASURING 646E AMPLIFIER AMPL/F/ER in 20 4 26 src/mo/v/zuva l /aREDUCTION -6AR 1 U/VCOA r50 STRIP TRANSMITTER Q 22 /&

MEMORY STANDARD TRANSMITTER DEV/CE PERMANENT--\ 'OR ne'er/v0- MAG/VET EA 00,4750 STRIP TRANSMITTER CONT OL NON-BALANCING POTE/VT/OMETERINVENTOR.

JOSEPH w. H1465,

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United States Patent 2,793,345 APPARATUS FOR MEASURING THE THICKNESS OFA COATING APPLIED TO A MOVING STRIP Joseph W. Hags, Irwin, Pa., assignorto United States Steel Corporation, a corporation of New JerseyApplication October 29, 1953, Serial No. 389,139

4 Claims. (Cl. 324-71) This invention relates to apparatus for measuringthe thickness of a coating applied to a moving strip and moreparticularly to apparatus for measuring the thickness of a zinc, lead,aluminum, paint, tin or other coating applied to a steel strip. Inapplying such a coating it is desired to know the exact thickness of hecoating as it is being applied since this enables the operator to adjustthe proc essing equipment to maintain the desired coating thickness. Toaccurately determine the thickness of the coating by the methods mostcommonly used it is necessary to cut a sample of standard area from thestrip and chemically dissolve the coating. Such methods are destructiveand time consuming so that in many instances the conditions existing atthe time the sample is taken change before the coating thickness isdetermined. Other types of apparatus used to determine coating thicknessalso have various disadvantages and are not applicable to all types ofcoating. One problem present in determining the thickness of a coatingon steel strip is to compensate for the normal variations in thicknessof the strip from one section to another which is often greater than thethickness of the coating being applied. Thus, while thickness gages suchas that shown in the patent to Rendel No. 2,474,117, dated June 21,1949, could be used to continuously measure the thickness of a coatedstrip and subtracting the nominal thickness of the uncoated striptherefrom to determine the coating thickness such determination would befar from accurate.

It is therefore an object of my invention to provide apparatus whichwill continuously and accurately measure the thickness of a coatingapplied to a moving strip. This and other objects will be more apparentafter referring to the following specification and attached drawings inwhich the single figure is a schematic view showing my device.

Referring more particularly to the drawings, the reference numeral 2indicates an uncoiler from which strip S is unwound. The strip S passesfrom the uncoiler through a coating unit 4 and pinch rolls 6 to a coiler8 where the strip is recoiled. Located adjacent the uncoiler 2 is a gage10 which may be a beta ray gage of a standard type or a gage such asshown in the patent to Rendel mentioned above. A similar gage 12 islocated adjacent the coiler 8. In many instances the strip passesthrough other processing equipment between the uncoiler 2 and coatingunit 4 so that the distance between the gages 10 and 12 may be as greatas several hundred feet. The conditions present in rolling steel stripare such that there is a definite variation in gage from one end of thestrip to the other and in a distance of several hundred feet thevariation in most instances would be thicker than the coating beingapplied. In order to take care of this difierence in gage I provide amemory device 14 which is rotated at a speed proportional to that of themoving strip. As shown, this is done by providing a mechanicalconnection 16 between the pinch rolls 6 and the memory device 14. Thisconnection is shown schematically and includes a synchronizing reductiongear control 42.

unit 18. The memory device 14 is of the electronic-' and relayed to atransmitter 22 adjacent the memory device 14 which translates theelectrical voltage into a magnetic impulse and applies the same to therecording disc of the memory device. The amplifier 20 is provided withpower from 110 volt A. C. supply lines 24. In like manner the gage 12provides an electrical impulse proportional to the thickness of thecoated strip which impulse is amplified by the amplifier 26 anddelivered to a second transmitter 28 which translates the electricalvoltage into a magnetic impulse and applies the same to the recordingdisc of the memory device. applied to the amplifier 26 from power line24. The memory device 14 rotates in the direction of the arrow and thedistance between transmitters 22 and 28 is proportional to the length ofstrip between gages 10 and 12. The reduction gear 18 is such that thememory device will rotate the distance between transmitters 22 and 28while the strip S is passing from the gage 10 to the gage 12. Atransmitter 30 is provided for applying a standard magnetic impulse tothe memory device 14. Power for the standard transmitter 30 is providedfrom power supply line 24 through a control 32 which reduces, thevoltage to magnetizing value. A receiver 34 is provided adjacent thetransmitter 28. The receiver 34 translates any magnetic impulse on thedisc of the memory device 14 and translates it into an electricalvoltage proportional thereto. This voltage is amplified by amplifier 36and applied to a thickness coating gage 38 which may be of theself-balancing potentiometer type. Power is applied to amplifier 36 andmeter 38' from the power supply lines 24. A magnetism eraser 40 isprovided adjacent the memory device 14 between the receiver 34 andtransmitter 30. This eraser 40 may be either a permanent or electrc-magnet. If electr c-magnet it is provided with power The operation ofthe device is as follows:

As the strip S passes through the line it is continuously gaged by thegages 10 and 12. At the same time the memory device 14 is rotated at aspeed proportional to to the disc of the memory device 14 by means ofthe transmitter 30. This impulse provides a given level on which themagnetic impulse from the transmitter 22 is, superimposed. A magneticimpulse from the transmitter 28 is superimposed on the magnetic impulsesalready on the memory device 14. However, this magnetic im+ pulse is ofopposite polarity to that already applied. The polarity can be reversedin many ways, such as by reversing the connections of the gage 12. Thestandard transmitter 30 may be omitted but is preferably provided inorder to provide a base of a definite amount on which the subsequentmagnetic impulses are applied. Since the time required for the memorydevice 14 to rotate the distance between the transmitters 22 and 28 isthe same as the time required for the strip S to pass from the gage 10to the gage 12 it will be seen that the impulse provided by thetransmitter 28 will always be superimposed on the impulse provided bythe transmitter 22 on the same increment of strip. Therefore, anyvariations in gage of the strip will not disturb the correct functioningof the device. Since the magnetic impulses are prm Patented May 21, 1957Voltage is from the supply lines 24 through a p rtiqnal 10,1119. trip.skasss, the oat galm e 38. ll always indicate the thickness of thecoating applied to the strip. If the coating is applied to only one sideof the strip this indication will be exact. If theoating is applied to;both sides of thestrip the meter 38- will be calibrated to indicate haltthe total thickness of both coatings,

While one embodiment of my-invention has been shown and described itwillbe apparent that other adaptations and modifications may be madewithout departing from the scope of the following claims;

Iclaim:

1. Apparatus formeasuring the; thickness of a coating pp ied to ovi asrin mp si a, fir eans. adjacentsaid strip for obtaining an electricalimpulse proportional to: thethicknessofthe'uncoated strip,- a secondmeansv remote from the first means adjacent said strip for obtaininganelectrical impulse proportional to the. thickness of the coated strip,means for subtracting said first impulse from said second impulse toobtain a net impulse proportional to coating thickness, means fordelaying the impression of said first impulse to said last named meansuntil that portion of the uncoated strip originally gaged reachessaid'second means, a meter, and means for impressing said, net impulseon said meter.

2. Apparatus for measuringthe thicknessxof a coating applied to a movingstrip comprising a first means adjacent said strip for obtaining anelectrical impulse proportional to the thickness of theuncoated strip, asecond means, remote from the first means; adjacent said strip forobtaining an electrical impulse proportional to the thickness of thecoated strip, a rotary memory device, means for rotating said memory.device at a speed proportional to that of the strip, a transmitter fortranslating the. electrical impulse from the first means into acorresponding magnetic impulse and applying it to said memory device, atransmitter for translating the electrical impulse from the secondmeansinto a corresponding magnetic impulse and superimposing the impulseonthe first impulse, said last named impulse being opposite in polarity tothe first impulse, said second transmitter being located from the firsttransmitter around said memory device in its direction of rotation adistance proportional to the distance between said first two means sothat an increment of strip will move from the first to the second meanswhile a point: on the memory device is rotating from. the first. tosecond transmitters, a receiver for receiving the net magnetic impulseand translating the same into an electrical voltage proportionalthereto, a meter, and means for impressing said last named voltage onsaid: meter.

3. Apparatus for measuring the tliickness ofa coating applied. to. amoving strip comprising a first means a'djacentsaid strip for obtainingan electrical impulse proportional to the thickness of the uncoatedstrip, a second means remote from the first means adjacent said stripfor obtaining an electrical impulse proportional to the thickness of thecoated strip, a rotary memory device,

ma s fo o at n s memory ev at a speed p o.- portional to that of thestrip, a transmitter for translating the electrical impulse from thefirst means into a corresponding magnetic impulse and applying it tosaid memory device, a transmitter for translating the electrical impulsefrom the second means into a corresponding magnetic impulse andsuperimposing the impulse on the first impulse, said last named impulsebeing opposite in polarity to the first impulse, said second transmitterbeing located from the first transmitter around said memory device inits direction of rotation a distance proportional to the distancebetween said first two means so that an increment of strip will movefromthe first to the second means while a point on the memory device isrotating from the first to the second transmitters, a receiver forreceiving the net magnetic impulse and translating the same into anelectrical voltage proportional thereto, a meter, means for impressingsaid last named voltage on said meter, and means located beyond saidreceiver inlthe direction of rotation of saidmemory device for erasingsaid magnetic impulses-from said memory device.

4; Apparatus for measuring the thickness of a coating applied to amoving strip comprising a first means adjacent said strip for obtainingan electrical impulse proportionaltto the thickness of the uncoatedstrip, a second means remote from the first means adjacent said stripfor. obtaining an electrical impulse proportional to the thickness, ofthe coated strip, a rotary memory device, means for rotating said memorydevice at a speed proportional to that of the strip, a first transmitterfor applying a standard magnetic impulse to said memory device, a secondtransmitterfor translating the electrical impulse from the first meansinto a corresponding magnetic impulse andsuperimposing the impulse onthe standard impulse, a third transmitter for translating the electicalimpulse from the second means into a corresponding magnetic impulse andsuperimposing the impulse on the first two impulses, said last namedimpulse. being opposite in polarity to the second impulse, said thirdtransmitter being located from the second transmitter around said memorydevice in its direction of rotation a distance proportional to thedistance between said first two means so that an increment of strip willmove from the first to the second means while a point on the memorydevice is rotating from the second to third transmitters, a receiver forreceiving the net magnetic impulse and translating the same into anelectrical voltage proportional thereto, a meter, means for impressingsaid last named voltage on said meter, and means located beyond saidreceiver in the direction of rotation of said memory device for erasingsaid magnetic impulses from said memory device.

References. Cited in the file of this patent UNITED STATES PATENTS1,163,678 Me'ssiter Dec. 14, 1915 1,895,113 Allen Jan. 24, 1933 2,527,002 Drake Oct. 24, 1950

